extended GatedGraphConv and NNConv to use AbstactGNNGraph#375

Ghaithq wants to merge 1 commit intoJuliaGraphs:masterJuliaGraphs/GraphNeuralNetworks.jl:masterfrom

Ghaithq:fix-issue-311Ghaithq/GraphNeuralNetworks.jl:fix-issue-311Copy head branch name to clipboard